The home secretary is blocking cabinet moves to make it easier for Chinese visitors to get visas, warning it would pose a national security risk and blaming poor visitor numbers on tourism chiefs not promoting Britain's natural beauty properly.

Theresa May's opposition is revealed in a leaked letter sent by her private secretary to Downing Street which emerged only a day after the culture secretary, Jeremy Hunt, tried to build on the Olympic success by unveiling an £8m marketing strategy to treble the number of Chinese visitors to Britain by 2015.

The issue appears to have sparked a clash between ministers at the highest levels of government. Hunt, backed by the business secretary, Vince Cable, and the chancellor, George Osborne, has led calls to simplify the visa regime for Chinese visitors after repeated and sustained complaints from the Chinese business community.

Chinese tour groups are currently able to apply for a single European Union visa, covering the 25 Schengen countries including France and Germany, but have to get a separate visa to visit Britain. Hunt said he want to use the Olympics to "turbocharge" Britain's tourism industry and told reporters one option was to design a "parallel process" whereby tour groups could apply for a British and EU Schengen visa at the same time.

But May is blocking any such move arguing that visa checks in Europe "do not match the UK decision quality" and claiming that British visa controls are a "key tool in protecting the public against significant harm".

Her letter leaked to the Daily Telegraph points out to Downing Street that there were already 400 Chinese criminals awaiting deportation and 1,000 asylum applications from Chinese citizens last year.

"The proposal … is not acceptable to the home secretary for national security reasons. At cabinet the issue of asylum claims was discussed," says the letter from May's principal private secretary, Katharine Hammond. "We also face significant challenges with foreign national offenders and organised crime, including drugs, money laundering, criminal finances, intellectual property, immigration and cybercrime."

May blames VisitBritain for failing to market Britain's scenic natural beauty and insists that the current visa system is not to blame for the UK's lack of popularity amongst Chinese visitors.

The home secretary criticises Hunt for using "selective statistics" to back up his claims that the visa system is to blame and says the costs involved are insignificant compared to the price and availability of hotels.

The Home Office declined to comment on the leaked letter but pointed out it had already made improvements to the Chinese visa services by introducing more staff, VIP facilities, an online application process, and translated guidance.

Sebastian Wood, the British ambassador in Beijing, wrote to May in June complaining that the UK visa system was seen in China as a "fortress" that was putting off tourists. The application forms are in English rather than Mandarin and cost nearly £100 to obtain compared with £55 to get permission to go to Spain.

The government is particularly keen to attract Chinese tourists because they are estimated to spend an average of three times more than other overseas visitors, but France receives 25-50% more Chinese tourists than the UK.